Adjustable coupler for electron tubes; adjustment made outside the vacuum and through a dielectric vacuum seal



Feb. 21, 1967 EVIN 3,305,799

M. E. L ADJUSTABLE COUPLER FOR ELECTRON TUBES; ADJUSTMENT MADE OUTSIDETHE VACUUM AND THROUGH A DIELECTRIC VACUUM SEAL Filed June 12, 1963 2sheetswsheet 1 BEAM CAVITY 670 i f '1 l r I i Z45C! H 190 f 43C! H 450 II 'F/G. 5 370 i F/G. 4 BY M ATTORNEY.

Feb. 21, 1967 M. E. LEVIN 3,305,799 ADJUSTABLE COUPLER FOR ELECTRONTUBES; ADJUSTMENT MADE OUTSIDE THE VACUUM AND THROUGH A DIELECTRICVACUUM SEAL Filed June 12, 1963 2 Sheets-Sheet 2 F/G. 6 I

l!| f/ I I K 7 MARTIN E. LEVIN INVENTOR.

ATTORNFY United States Patent 3,305,799 ADJUSTABLE COUPLER FOR ELECTRONTUBES; ADJUSTMENT MADE OUTSIDE THE VACUUM AND THROUGH A DIELECTRICVACUUM SEAL Martin E. Levin, Burlingame, Califi, assignor, by mesneassignments, to Varian Associates, a corporation of California FiledJune 12, 1963, Ser. No. 287,322 2 Claims. (Cl. 33324) This inventionrelates generally to electron tubes'and more particularly to couplersfor transferring energy bebetween one electromagnetic circuit, such as aresonant cavity of the type employed with an electron tube andassociated circuits.

As is well known, energy is introduced into and extracted from resonantcavities and other electromagnetic energy circuits in .a large number ofways. The energy may be extracted through an appropriately locatedopening formed in the wall of the circuit element or cavity.Alternatively, the energy can be extracted by an inductive loopcoupler.-

When the resonant cavity or circuit element forms a portion of anevacuated envelope, then there are added complications. If an opening isused to couple energy out of the cavity, a sealed window must beprovided. The window must be made of suitable dielectric material andhave suitable structure to minimize reflections of the electromagneticenergy passing therethrough; it must be able to withstand the heatingeffects to which it is subjected; and it must form a competent seal withthe ad jacent envelope portion.

Induction loops can be employed for coupling into a cavity or othercircuit element. However, if adjustment is desired, then resort must behad to relatively complicated arrangements. Where the cavity forms partof the evacuated envelope, bellows, movable seals and the like arerequired for tuning or adjusting the inductive loop. Such arrangementsare relatively cumbersome and increase the risk of leaks in theevacuated envelope.

It is, therefore, an object of this invention to provide an improvedcoupler for electromagnetic energy.

It is another object of the present invention to provide a coupler forresonant cavities.

It is a more particular object of this invention to provide an improvedadjustable load coupler suitable for use with resonant cavities of thetype which form a portion of an evacuated envelope.

It is another object of this invention to provide an adjustable loadcoupler of the aforementioned character in an evacuated envelope.

It is still another object of this invention to provide companyingdrawings in which:

FIGURE 1 is a view partially in elevation and partially in cross-sectionof a klystron type of electron tube employing a coupler in accordancewith this invention;

FIGURE 2 is an enlarged view of one coupler shown in FIGURE 1;

FIGURE 3 is an equivalent circuit of the coupler shown in FIGURE 2;

FIGURE 4 is a view somewhat similar to FIGURE 2 but showing a couplerproviding parallel rather than series tuning;

which eliminates the requirement for moving parts with- V r .phere.

FIGURE 5 is an equivalent circuit of the coupler shown in FIGURE 4;

FIGURE 6 shows an adjustable inductive couplerhaving a single sealformed with the envelope; and

FIGURE 7 shows another embodiment of a coupler in accordance with FIGURE6.

Referring to FIGURE 1, one type of electron device to which theinvention is applicable is illustrated. The device is a klystron 11including a gun 13, a plurality of cavities 15, 17 and 19 connected bydrift tube sections 21, 23 and 25, and a collector electrode 27. Thedrift tube sections 21, 23 and 25 are separated by interaction gaps 29,31 and 33 within each of the cavities 15, 17 and -19 The gun 13 producesa focused beam of electrons which is directed axially through the drifttube sections toward the collector electrode. Electron flow isaccomplished by maintaining the drift tube sections and the collectorelectrode at a positive electrical potential with respect to the cathodeof the gun 13.

next gap 31, it excites the cavity 17 which excitation, in

turn, produces additional modulation and further bunching of theelectrons in the beam. As the bunched electrons cross the gap 33, theoutput cavity 19 is excited.

The amplified energy may be extracted from the output cavity by anadjust-able load coupler 37 in accordance with the present invention.The input cavity may also employ an adjustable load coupler inaccordance with the invention.

A coupling device in accordance with the invention is shown in moredetail in FIGURE 2. A coaxial transmission line 45 including outerconductor wall 46 and center conductor 47 isshown mounted with the outerconductor to the cylindrical wall 43 of the cavity 19. The wall 46 ofthe coaxial line is, therefore, electrically connected to the cavitywalls (plate wall sections 39, 41 and cylindrical wall sections 43 inFIGURE 1) to form a common ground plane. A dielectric disc-like member50 forms and envelope portion and permits electrical energy to travelfrom within the cavity to the coaxial transmission line.

be formed, for example, by metallizing the end portion of the tube 51.

The open end of the tube' may be open to the atmos- In the embodimentshown, however, the open end includes a metallic cover 55 provided witha threaded opening 57 which threadably receives metal stud 59. The outerend of the stud is formed to receive an adjusting tool, for example, itmay be slotted as shown at 61 to accommodate a screwdriver. The innerend includes a metal member 63 which conforms geenerally in shape withthe adjacent surface of metal plate 53. Stud '59 and plate 63, together,then form a plunger which is movable with respect to the metallic plateor member 53.

It is apparent that by screwing the stud 59 in an out of the cover 55,the capacitance between the metal plate 53 and member 63 is varied.Since the member 63, stud 59 and plate 55 are metal, the member 63 thenis electrically connected to the cavity walls, the common ground. Plate53, on the other hand, is connected at 65 to the inner conductor of thecoaxial transmission line by the loop 67.

The equivalent circuit of FIGURE 3 represents the tuner shown in FIGURE2. Operation of the adjustable load coupler is more clearly apparentfrom a review of FIGURE 3. The cavity is designated by a resonantcircuit 19 including a capacitor, inductor and the electron beam, shownadjacent the capacitor, which represents the gap 33. The inductive loop67 of FIGURE 2 is shown in FIGURE 3 as a coil L The capacitor formed bythe plates 53 and member 63 of FIGURE 2 is shown in FIGURE 3 as avariable capacitor C connected between the coil L and ground. The otherside of the coil L is connected to the center conductor of the coaxialtransmission line 45. The combination just described provides means forcoupling energy from the beam into the coaxial transmission line. Thecavity and coupling loop cooperate to provide, in effect, an impedancetransformer whereby the impedance of the beam is transformed to a valuewhich corresponds generally to the impedance of the coaxial line tomaximize transfer of energy from the beam to the line. In general, thebeam impedance is transformed to an impedance of the order of thecoaxial transmission line impedance. However, the adjustable coupler ofthe present invention provides means for obtaining a more precise matchof impedance to achieve maximum energy transfer.

Adjustment of the coupler can be made without having any moving partswithin the evacuated cavity. The degree of adjustment for a givenmovement may be varied by altering the size of the member 63 and/orplate 53.

A tuned coupler of the type described is preferably employed inconjunction with the output cavity.

Referring now to FIGURES 4 and 5, a parallel tuned coupler rather than aseries tuned coupler is shown. This type of coupler is preferablyemployed with the input cavity to apply the signal thereto or may beemployed for loading intermediate cavities. In this instance, the tuningelement 37a is similar to the element 37 of FIG- URE 2 but is located inthe circuit to provide a capacitance between ground and the centerconductor 47a of the coaxial transmission line 45a. In the embodimentshown in FIGURE 4, the capacitive coupling is bet-ween the member 630and the center conductor 47a of the coaxial transmission line. Ametallic member similar to member 53 may be added to line 47a toincrease the parallel capacitance if required.

Referring to FIGURE 5, an equivalent circuit of the coupler of FIGURE 4is shown. The resonant cavity is shown as the resonant circuit 19a, andthe loop 67a is shown as the inductance L The capacitance C in parallelwith the inductance L incorporates the member 63a and the line 47a. Boththe inductor L and the capacitor C are connected to the center conductorof the coaxial line 45a. Again, by adjusting the position of the member63a, the capacitance C is varied and, therefore, the impedance of theinput coaxial line is matched to the impedance of the beam through theimpedance transformation introduced by the combination of the inputcoupler and resonant cavity.

The adjustable coupler shown in FIGURE 6 is simpler in construction thanthe couplers described above because it employs a single vacuum seal.The coupler shown includes a coaxial transmission line 71. Thetransmission line includes an outer conductor including a first portion72 which is sealed to the envelope, a second portion 73 which isthreadably received by the first portion whereby the second portion canbe moved axially with respect to the first portion, and a third portion74 is the end of an associated coaxial line. The portion 74 is insliding electrical contact with the movable portion 73.

A dielectric window 76, such as a ceramic disc, is suitably sealed tothe envelope by well known means to form with the associated envelopeportions the evacuated envelope for the the electron tube. A metal plate77 is carried by the inner surface of the window. The plate may, forexample, be formed by metallizing onto the surface of the window. Acoupler loop 78 has one end attached to the metal plate and its otherend suitably connected to the metal envelope of the electron tube.

The coaxial line 71 includes an inner conductor which is formed with afirst portion 81 which is supported by a dielectric window 82 suitablycarried by the movable outer conductor portion 73. The end of the innerconductor 81 is provided with a plate 83 which cooperates with the plate77 to form a variable capacitor. It is seen that by rotation of theouter conductor portion 73, it is moved axially to thereby adjust therelative spacing of the plates 77 and 83 and, therefore, the capacitancein series with the center conductor of the transmission line.

The upper portion of the center conductor 81 includes an opening orrecess 84 adapted to slidably receive the portion 86 of the associatedcoaxial line to provide electrical contact but permit axial movement ofthe inner conductor 81.

It is apparent that the mechanical means illustrated are merelysuggestive of a possible means providing an axially adjustable innerconductor and that other mechanical configurations may be employed.

However, it is to be observed that only a single ceramic to metal sealis required to form the envelope and that the capacitive adjustment orimpedance matching adjustment is external of the envelope.

In certain applications where the coupler need not be adjustable, forexample, in instances where the coupler elements can be designed to givethe desired impedance match, the concept of coupling through adielectric window is still important. Referring to FIGURE 7, there isshown a coupler similar to that shown in FIGURE 6. Like referencenumerals are used for like parts. The coupling between theelectromagnetic circuit and the associated transmission line is achievedwith the combination of the loop 78a having a metallic element 77asupported by the dielectric window 76a. A second metallic element 83a issecured to the other side of the window. The metallic elements andwindow form a capacitor which couples the energy from the first circuit78a to the coaxial transmission line 71. It is apparent that thecapacity can be designed to have the correct value by controlling thesize of the metal plates, and the material and thickness of thedielectric window.

Thus, it is apparent that a new coupler has been provided. It solves thelong standing problem of permitting adjustment of the coupling between abeam, cavity and associated transmission line in an electron device,such as an integral cavity klystron. Adjustment of the coupling iseffected without use of moving parts within the cavity. The tuning maybe of the series or parallel type. The adjustment provides means formatching the coaxial line and beam impedances. A minimum number of sealsis required whereby the danger of leaks in an evacuated envelope issubstantially reduced.

I claim:

1. An adjustable coupler for extracting energy from an electromagneticcircuit of the type having a conductive wall defining an electromagneticenergy confining circuit comprising a loop insulated from said wall anddisposed in said circuit in coupled relationship to the fields of theelectromagnetic energy, and connected directly to the center conductorof a coaxial output transmission line, a cylindrical dielectric memberhaving an open end mounted on said wall and a closed end extending intosaid circuit, a 1st conductive member disposed within said cylindricaldielectric member and mounted directly on said conductive wall for axialmovement with respect to said dielectric member, and a 2nd conductivemember 5 afiixed to said dielectric member and to one end of said loop,said 2nd conductive member being capacitively coupled through thedielectric member to said 1st conductive member whereby the capacitancebetween said 1st and 2nd conductive member is variable and placed inseries with said loop.

2. In an electron tube of the type employing at least one resonantcavity a load coupler for coupling energy between said resonant cavityand an associated circuit comprising a loop disposed within andinsulated from said cavity and coupled to the electromagnetic fields inthe cavity, said loop connected directly to the center conductor of acoaxial output transmission line, a cylindrical dielectric member havingan open end mounted on the cavity wall and a closed end within thecavity, a 1st conductive member disposed within said cylindricaldielectric member electrically and mechanically connected directly tothe walls of said cavity for axial movement with respect to saiddielectric member, and a 2nd conductive 6 member affixed within thecavity to said dielectric member and to one end of said loop, said 2ndconductive member being capacitively coupled through the dielectricmember to said 1st conductive member.

References Cited by the Examiner UNITED STATES PATENTS 2,311,520 2/ 1943Clifford 333-83 2,312,929 3/1943 Litton 333-83 X 2,404,085 7/1946 Okresset a1. 333-24 2,414,785 1/1947 Harrison et al 33383 X 2,547,412 4/ 1951Salisbury 325-445 FOREIGN PATENTS 128,603 1960 U.S.S.R.

HERMAN KARL SAALBACH, Primary Examiner. R. D. COHN, Assistant Examiner.

1. AN ADJUSTABLE COUPLER FOR EXTRACTING ENERGY FROM AN ELECTROMAGNETICCIRCUIT OF THE TYPE HAVING A CONDUCTIVE WALL DEFINING AN ELECTROMAGNETICENERGY CONFINING CIRCUIT COMPRISING A LOOP INSULATED FROM SAID WALL ANDDISPOSED IN SAID CIRCUIT IN COUPLED RELATIONSHIP TO THE FIELDS OF THEELECTROMAGNETIC ENERGY, AND CONNECTED DIRECTLY TO THE CENTER CONDUCTOROF A COAXIAL OUTPUT TRANSMISSION LINE, A CYLINDRICAL DIELECTRIC MEMBERHAVING AN OPEN END MOUNTED ON SAID WALL AND A CLOSED END EXTENDING INTOSAID CIRCUIT, A 1ST CONDUCTIVE MEMBER DISPOSED WITHIN SAID CYLINDRICALDIELECTRIC MEMBER AND MOUNTED DIRECTLY ON